Aircraft auxiliary jet engine nacelle



Oct. 22, 1957 P. G. FANDEUX 2,810,534

AIRCRAFT AUXILIARY JET ENGIN NACELLE Filed April 16, 1954 Inventer PMWW byfiWrW United State AIRCRFT AUXILIARY JET ENGINE NACELLE Application April 16, 1954, Serial No. 423,737 Claims priority, application France April 24, 1953 4 Claims. (Cl. 244-58) This invention relates to auxiliary jet engines used as an aid or as a substitute for normal propelling means of an aircraft, i. e. provided for operating within short periods of time and at a comparatively low speed of the aircraft e. g. during take-off or in the case of a failure of said normal propelling means.

Auxiliary jet engines of this type are housed in a small streamlined nacelle under the fuselage of the aircraft. The air intake for feeding the jet engine is constituted by a pipe leading to the inlet of the compressor of the jet engine. Usually, the mouth of said pipe is located in the nose of the nacelle and faces directly the relative wind. known air intakes is practically equal to unity, whatever may be the speed of the aircraft and both when the jet engine operates and when it is at rest. In the last condition, this efficiency is objectionable since the air rushing into the air intake causes autorotation of the compressor 'at a nunibr of turris Whi'ch increases Withthe speed of the aircraft, thus causing' unwanted wear and undue increase of the drag.fl Moreover,.when .itrains, water is forcd with ir intb'th'jet engine, which'has obvious drawbacks. Similarly, the front position of the mouth of the intake facilitates introduction of extraneous bodies such as stones when the aircraft rolls on the ground. Briefly, it is obvious that a good air-conducting eificiency is required only when the auxiliary jet engine operates i. e. during comparatively short lime periods, while in any other condition, air penetration is to .be avoided.

Various devices have been proposed heretofore for closing the air-intake of the auxiliary jet engine nacelle when said engine is not in duty. Unfortunately, all these devices as well as the controls are complicated and expensive. Moreover, they increase unduly the weight of the nacelle and, last but not least, they give rise, or are subject, to icing phenomena, so that they must be provided with pre-heating facilities or other de-icing means.

This invention has for its purpose to overcome the abovementioned drawbacks of the conventional airin takes without resorting to any mechanical obturating means.

The main object of the invention is, therefore, to provide an auxiliary jet engine of the type described with an air intake having its mouth opening inthe streamlined wall of the jet engine nacelle, at such a distance from its nose and having its edge, and in particular, the trail ing portion of said edge, so shaped that the air-flow resulting from relative Wind, instead of naturally tending to enter said mouth is projected further downstream along the streamlined outline of the nacelle.

Another object of the invention is to dispose the air intake opening upstream the maximum cross-section of the nacelle, so that it is located in a zone wherein the boundary layer has its maximum thinness.

With these arrangements, practically no airenters the intake when the jet engine is at rest, the boundary layer,

The air conducting efiiciency of such aten acting in front of theintake mouth as a kind of obturating air sheet, as long as air is not deviated into the intake under suction due to operation of the jet engine.

This ofiers a number of advantages:

The jaractical absence of air circulation when the jet engine does not operate avoids any substantial autorotation of the compressor of said engine. The additional drag of the engine nacelle is reduced, as tests have shown, by about 25% as compared with that of a nacelle equipped with a front air intake, other things being equal. The ignition of the engine, when the aircraft is flying, takes place without any dificulty, even under violent rain. In spite of the aerodynamc quasiobturafion of the air intake mouth, the air conductiug efficiency of the air intake when the jet engine is in operation is suificient at comparatively low speeds which are solely that the airconducting elficiency is kept at a value substantially equal to unity, up to a speed of about miles per hour. 7 r

In spite of their capacity of increasing the air conducting efliciency when the jet engine is operating, the above mentioned longitudinal panels do not impair the main property of the air intake according to the invention i. e. that of allowing practically no natural introduction of airinto the jet engine when the same is at rest. a

-,Aqnore particular object of the invention is te dispose {the mouthof the air intake under the nacelle with-- its longitudinal axis in the mid vertical plane of the same.

This disposition has proved to be the best one for avoiding the penetration of water into the jet engine during rainy weather.

Other objects and advantages of the invention will be apparent from the following detailed description together with the accompanying drawings in which an embodiment of the invention has been shown as a mere illustration.

In these drawings:

Fig. 1 is a perspective view of an airplane equipped with an auxiliary jet engine having an air intake according to the invention.

Fig. 2 is a sectional view of the front half of the nacelle of the auxiliary jet engine showing the air intake according to the invention in longitudinal axial section.

Fig. 3 is a front view of said nacelle and,

Fig. 4 is an under plane view of the same.

In Fig. 1, the fuselage 1 of an airplane, normally pro pelled by two air-screw engines 2, carries under the lowest portion of its outer wall a streamlined nacelle 3 which is secured on said wall through a streamlined vertical mast 4 and which is provided with an air intake according to the invention, the mouth of which is generaliy shown in Fig. 1 at 5.

According to the invention, as shown in Figs. 2 to 4, the air intake 5 of the jet engine 6 has its leading edge 5a located at a distance L from the tip of the streamlined nose 3a of nacelle 3 at which distance the impact of the air on the profile of the nacelle takes place with an angle of incidence suflicienfly small t0 cause the air threads to creep along said profile in a very thin layer, known as the boundary layer. Moreover, the trailing edge 5b of the intake mouth 5 is preferably rounded as shown in Fig. 2, so as to direct the air flow further down stream along the outer profile of the nacelle, while opposing its penetration into the air intake.

It has been found that for a ratio D being the diameter of the maximum cross-section of the nacelle, the air penetration into the air intake is negligible or at least insufiicient to cause any consider able autorotation.

The air intake proper is consituted by a pipe 7*connecting the above describedmouth 5 With the inlet of the compresser et the auxiliary jet engine 6. From the point of view of air conducting efliciency, the inclination a et the axis of the rectilinear portion of pipe7; with respect to the longitudinal axis XX of the nacelle should be made as small as possible.

On theother hand, it is obvious that the overall length of the nacelle depends upon thevalue of said angle, so that a suitablecompromise is adopted in practice for each particular case; In a specific embodiment it has been found that an angle acf 30 corresponds to a reasonable length of the nacelle; The above mentioned rectilinear portion of pipe 7 is connected With the inlet of engine 6 through a suitablyincurved portion, the *latter'being secured on engine 6 through anvsuitable-means, as shown at 8. In the example shown, mouth 5 of the air intake is laterally straddled by a pair of parallellongitudinai panels 9 of comparatively-small width arranged symmetrically on either side 'of mouth -5, slightly shifted-rearwardly With respect thereto and having substantially the same 1. In an airplane having a fuselage, an auxilaty streamlined jet engine nacelle having a transverse crosssection which varies in the fore and aft direction fixedly secured under said fuselage considered in the normal attitude of the airplane, an air intake including air conducting means to feed said jet engine with externat air and a mouth for said air conducting means opening in the outer wall of said nacelle, the leading edge of said mouth being located at a distance from the tip of the nose of said nacelle at least equalto half the diameter of the maximum transverse cross-section of said nacelle, While the trailing edge of said mouth is located upstream said maximum transverse cross-section and presents a slightly rounded profile.

2. A streamlined engine nacelle according to claim 1, further provided with longitudinal panels extending on either side of said air intake mouth to canalile air flow and to improve the air conducting eificiency of said air intake under suctionfromsaid engine.

3. A streamlined engine nacelle according to claim 1, further provided With longitudinal panels extending on either side of said air.intake mouth, having a Iength substantially equal to that of said mouth and slightly shifted rearwardly With respect to the same.

4. A streamlined engine nacelle according to claim 1, wherein, in the normal attitude et the airplane, said air intake mouth is located under said nacelle with its plane substantially right-angled with the main vertical plane et said nacelle.

References Cited in the file lot this patent UNITED STATES PATENTS Re. 23,198 Anxionnaz Feb. 21, 1950 1,980,233 Stout Nov. 13, 1934 2,477,637 Mercier Aug. 2, 1949 FOREIGN PATENTS 612,796 Great Britain' Nov. 17, 1948 993,078 France July 18, 1951 OIHER REFERENES Aviation Issue of October, 1945; pp. 172, 173. 

